Diced electronic devices are usually mounted on a receiving plate in such a way that their leads or electrical contact points face away from the plate. After picking up these devices from the receiving plate, the devices often have to be flipped so that subsequent processes such as functional testing or visual integrity checking can be performed on them.
Prior art methods have been developed to flip electronic devices before transferring them to processing stations for subsequent processes.
For example, U.S. Pat. No. 6,171,049 describes using an intermediate station for flipping a work-piece. In particular, a first head of a transfer unit is used to pick up the work-piece from the receiving plate and subsequently, the work-piece is brought to the intermediate station where it is flipped. A second head of the transfer unit then picks up the work-piece in this flipped position and transfers it to a processing station.
Further, WO2007057291 describes using a turntable for inverting electronic components. This turntable includes four locations, namely, a location (A) for loading the electronic components, a start-of-inversion location (B), an end-of-inversion location (C) and a location (D) for discharging the components from the turntable. An inverting device actuated by a fixed rotating motor is used to invert the electronic components between the start-of-inversion location (B) and the end-of-inversion location (C).
JP2012119494A describes using a vertical indexing wheel with extensible pick heads. Each pick-head retrieves a work-piece from a receiving plate and since the wheel rotates vertically, the electronic components are flipped as the wheel turns.
FIG. 1 shows another prior art apparatus 100 capable of flipping electronic devices before transferring them to processing stations 116. In particular, the apparatus 100 comprises a vertically rotating module 104 having a first main body 106 and a plurality of first pick heads 108, and a horizontally rotating module 110 having a second main body 112 and a plurality of second pick heads 114. Electronic devices are retrieved one at a time from the receiving plate 102 by the first pick heads 108. The electronic devices are flipped as the first main body 106 rotates. Hence, when the first pick head 108 reaches the position 109 via the rotation of the first main body 106, the electronic device it is carrying is in the flipped orientation. A second pick head 114 in the position 115 then retrieves the electronic device in the flipped orientation. Via a rotation of the second main body 112, the electronic device is transferred in this flipped orientation to the processing stations 116.
Although the prior art methods described above are able to flip the electronic devices, they involve multiple transfers of the electronic devices and this can lead to potential problems. For example, referring to the apparatus 100, each electronic device has to be transferred twice—once from the receiving plate 102 to a first pick head 108 and another time from the first pick head 108 to a second pick head 114. One problem arising from this is that each time the electronic device is transferred, there is a chance that the electronic device is not situated in the center of the pick head 108, 114 where the suction hole is. This increases the risk of dropping and hence, damaging the electronic device. This risk is higher when handling smaller electronic devices if the pick heads 108, 114 have suction holes that are so small that a slight offset of the electronic devices from their centers will cause the suction holes to be severely misaligned with respect to the devices.
A further problem with the apparatus 100 is that the distance between the center of the first main body 106 and each of the first pick heads 108 may vary. Similarly, the distance between the center of the second main body 112 and each of the second pick heads 114 may also vary. This is due to fabrication errors and errors introduced when the pick heads are changed (such changes are performed so as to handle different devices e.g. devices having different sizes and characteristics). Therefore, there is a chance that some of the first pick heads 108 may not centrally retrieve the electronic devices. Furthermore, the first pick head 108 at position 109 and the second pick head 114 at position 115 may not be aligned and this may cause the electronic device retrieved by the second pick head 114 to be offset from its center (even if the device was correctly picked at the center of the first pick head 108). As a result, the electronic device may drop. Manual adjustments of the positions of the pick heads 108, 114 are thus often needed. However, such adjustments require highly skilled workers and are extremely time consuming. Moreover, the chances of dropping an electronic device increase as the size of the electronic device decreases. Thus, it is especially risky for the apparatus 100 to handle very small electronic devices, in particular, those with a pick-up surface area of 0.6 mm×0.3 mm or less.